Composition to me is the means of writing in a way that is convincing and at the very least gives the reader an understanding of the point being made. It is something that is not easy to learn and can take a person years to learn, and good composition also often takes several rewrites in order to make it more convincing. It is different from creative writing, or writing to life, since that form of writing does not necessary require the writer to be working to prove a point. At it's heart, composition is a form of communication. The writer is expressing their ideas about a given topic and explaining their views regarding it. Composition is something that exists for all subjects, as all subjects have times where the scholar means to present a particularly point and argue it. Judging by the Yancey reading, it's a more social from of communication, and can have a form of spontaneity.
While people tend to conceive of writing and composition as lonely, secluded tasks, or simply something performed in a long format, but that definition is changing as people find new and different ways to communicate though the various forms of social media. Composition is more and more essential, because composition, regardless of how we tend to view reading as more important, is the essential tool that we have in order to communicate with one another, and to present ideas to one another, whether they are carefully formatted essays, or simple memes meant to entertain, all of these give some kind of point of idea that is being expressed.
While people tend to conceive of writing and composition as lonely, secluded tasks, or simply something performed in a long format, but that definition is changing as people find new and different ways to communicate though the various forms of social media. Composition is more and more essential, because composition, regardless of how we tend to view reading as more important, is the essential tool that we have in order to communicate with one another, and to present ideas to one another, whether they are carefully formatted essays, or simple memes meant to entertain, all of these give some kind of point of idea that is being expressed.